Ultrasonic wave type alarm device

Abstract

An ultrasonic wave type alarm device is provided with a narrow band filter for passing only a Doppler effect signal of a human body, and a quick discharge type integration circuit for removing the effect of a Doppler effect signal of a small animal other than the human body, thereby to carry out an alarm operation correctly.

I claim: 
     
       1. In an ultrasonic alarm system of the type having an ultrasonic wave transmitter for transmitting ultrasonic waves through air; an ultrasonic wave receiver for receiving ultrasonic waves having Doppler effect frequency components; and a detector circuit for developing electrical Doppler frequency signals; the improvement which comprises: a. a first bandpass filter receptive of the Doppler frequency signals developed by said detector circuit and having a narrow pass band effective to pass only Doppler frequency signals having frequencies characteristic of certain human motions;   b. a first quick discharge integrator circuit for integrating the output Doppler frequency signals from said first bandpass filter;   c. a second bandpass filter receptive of the Doppler frequency signals developed by said detector circuit and having a narrow pass band within the frequency band of said Doppler frequency signals and without the pass band of said first bandpass filter;   d. a second quick discharge integrator circuit for integrating the output Doppler frequency signals from said second bandpass filter; and   e. a comparator receptive of the outputs from said first and said second quick discharge integrator circuits.   
     
     
       2. In an ultrasonic alarm system according to claim 1, wherein said comparator comprises a differential amplifier. 
     
     
       3. In an ultrasonic alarm system according to claim 1, further comprising an alarm enabled by electrical signals above a certain threshold value, and means for applying the comparator output to said alarm. 
     
     
       4. In an ultrasonic alarm system according to claim 1, wherein said quick discharge circuits each comprise: a capacitor; a resistor connected to said capacitor for applying the output Doppler frequency signals from a respective one of said bandpass filters to charge said capacitor; a diode connected in parallel with said resistor and connected having a polarity relative to the charge stored in said capacitor to conduct in the absence of a Doppler frequency signal applied to said resistor; and a second resistor connected to a junction of said first resistor and said diode for providing a discharge path when said diode is conductive. 
     
     
       5. In an ultrasonic alarm system according to claim 1, wherein said transmitter develops ultrasonic waves having a frequency on the order of 40 Kilohertz, one of said bandpass filters has a pass band from about 80 Hz to about 180 Hz, and the other of said bandpass filters has a pass band within the range of about 800 Hz to 1100 Hz. 
     
     
       6. In an ultrasonic alarm system of the type having an ultrasonic wave transmitter for transmitting ultrasonic waves through air; an ultrasonic wave receiver for receiving ultrasonic waves having Doppler effect frequency components; and a detector circuit for developing electrical Doppler frequency signals; the improvement which comprises: a. a bandpass filter receptive of the Doppler frequency signals developed by said detector circuit and having a narrow pass band effective to pass only Doppler frequency signals having frequencies characteristic of certain human motions; and   b. a quick discharge integrator circuit for integrating the output Doppler frequency signals from said bandpass filter; and   c. wherein said ultrasonic wave transmitter comprises an electroacoustic transducer having a directivity pattern with a wide dimension in the direction of movements of a moving object to be detected, and having a narrow dimension in directions different from the direction of the movements to be detected.   
     
     
       7. In an ultrasonic alarm system of the type having an ultrasonic wave transmitter for transmitting ultrasonic waves through air; an ultrasonic wave receiver for receiving ultrasonic waves having Doppler effect frequency components; and a detector circuit for developing electrical Doppler frequency signals; the improvement which comprises: a. a bandpass filter receptive of the Doppler frequency signals developed by said detector circuit and having a narrow pass band effective to pass only Doppler frequency signals having frequencies characteristic of certain human motions; and   b. a quick discharge integrator circuit for integrating the output Doppler frequency signals from said bandpass filter; and   c. wherein said ultrasonic wave receiver comprises an electroacoustic transducer having a directivity pattern with a wide dimension in the direction of movements of a moving object to be detected, and having a narrow dimension in directions different from the direction of the movements to be detected.